Working memory has been dubbed the heart of intelligent behavior, and a core property of this critical cognitive system is its highly limited capacity. Working memory capacity limitations are reliably associated with individual differences in many basic forms of cognition (e.g., language and mathematical abilities), and working memory deficits have been observed in at-risk populations, including children diagnosed with attention-deficit/hyperactivity disorder, autism, and children born preterm. Given these influences, understanding the development of working memory capacity limits has broad implications and may be critical to intervention efforts with atypically developing children. This grant focuses on the development of a central type of working memory called visual working memory (VWM). VWM plays a key role in much of visual cognition, comparing percepts that cannot be simultaneously viewed and identifying changes in the world when they occur. Research has shown that VWM develops dramatically between infancy and 5 years old, and a recent dynamic neural field (DNF) model of VWM has formalized a candidate neural mechanism for how VWM capacity changes in early development and why such changes vary across tasks. A key goal of the grant is to test this theoretical account at neural and behavioral levels. In particular, we will conduct an accelerated longitudinal study from 6 months to 4.5 years. At each age, children will complete two functional neuroimaging sessions and a structural neuroimaging session. We will use these data to examine: (1) whether the DNF model captures individual developmental trajectories in VWM performance from 6 months to 4.5 years; (2) whether the DNF model predicts functional changes in the VWM brain network in early development; and (3) whether changes in DNF parameters over development are explained by localized changes in myelin content within the VWM network. Results from this grant will set the stage for extensions of our approach to examine longitudinal changes in at-risk populations. This work will also foster an innovative approach to individualized interventions guided by a neural process model of VWM that speaks to individual differences in both brain and behavior.